Mohamed Salah faces a fight to play in any of Egypt's World Cup group games, according to one of Liverpool's physiotherapists.
Club physio Ruben Pons has estimated Salah would normally need "three to four weeks" to recover from the left shoulder injury he sustained during Saturday's Champions League final against Real Madrid.
A three-week absence would keep Salah out of action until June 19 while four weeks would see the forward sidelined until June 26, the day after Egypt's last group game. Salah may also then need to regain a degree of match fitness.
Egypt's opening fixture in Group A is against Uruguay on June 15. They then face Russia on June 19 and Saudi Arabia on June 25.
"He is sad about what happened but he is totally focused on recovery and seeing when he can be ready," Pons told Spanish daily, Marca.
"In principle it will be three to four weeks but we are going to try to reduce those deadlines, that's the big goal."
Salah has flown to Spain to undergo treatment, accompanied by doctors from both Liverpool and the Egyptian national team.
The 25-year-old had to be substituted during the first half of Liverpool's defeat in Kiev after being pulled to the ground by Sergio Ramos.
He left the field in tears but appeared more optimistic on Sunday, when he wrote on Twitter: "It was a very tough night, but I'm a fighter.
"Despite the odds, I'm confident that I'll be in Russia to make you all proud. Your love and support will give me the strength I need."
Egypt star Salah to travel to Spain for treatment
Liverpool and Egypt star Mohamed Salah will travel to Spain on Tuesday for treatment on the injured shoulder that wrecked his Champions League final bid and threatens his World Cup participation.
Egypt's football federation (EFA) said Salah's entourage had chosen Spain for a rehabilitation programme that Egyptians will hope helps Salah return in time for next month's World Cup in Russia.
According to an EFA statement Salah will be accompanied by Liverpool's medical staff "for the duration of the treatment period", having "started his rehabilitation on Sunday".
Salah, who hit a stunning 44 goals for Liverpool last season in all competitions, was forced out the Champions League final in tears on Saturday clutching his left shoulder after being wrestled to the ground by Real Madrid captain Sergio Ramos.
It was feared the injury had ruled Salah out of the June 14-July 15 World Cup, but on Sunday the Reds' striker said he was "confident" he would be back in time.
"It was a very tough night, but I'm a fighter. Despite the odds, I'm confident that I'll be in Russia to make you all proud," Salah wrote on his official Twitter account on Sunday.
Egyptian media reported Salah wouldn't kick a ball in anger for three weeks.
Egyptian federation officials meanwhile are set to pay Salah - described by the EFA as "the symbol of Egypt" - a morale-boosting visit on Wednesday.
Egypt, who were drawn in Group A, open their World Cup campaign against Uruguay on June 15, before facing hosts Russia and Saudi Arabia.
The Pharaohs play a first warm-up match, against Colombia, in Bergamo, Italy on June 1.
Salah injury 'serious', says Liverpool boss Klopp
Liverpool manager Jurgen Klopp revealed that Mohamed Salah's injury that forced him off in the first half of the Champions League final on Saturday was "serious".
"It is a serious injury. He is in hospital for an X-ray. It is either the collarbone or the shoulder itself," Klopp said after Liverpool's 3-1 defeat to Real Madrid in the final in Kiev.
"It doesn't look good. That's it."
Salah, who scored 44 goals for Liverpool this season, came off just half an hour into the game in tears after hurting himself in a challenge with Sergio Ramos.
Liverpool had been on top at that point, but following the shock of the Egyptian's injury they went on to lose due to a combination of two goalkeeping howlers by Loris Karius and a superb Gareth Bale goal.
However, Klopp believed losing Salah was the turning point.
"Of course it was a big moment in the game. I know if you say that after you lost it sounds like you're a bad loser, but for us it was like a harsh challenge. It was like wrestling.
"The shock of the boys was obvious."
Klopp admitted that Salah now risks missing out on the World Cup - he has been hoping to lead Egypt in their first appearance at the tournament since 1990, but their opening match is against Uruguay on June 15, less than three weeks from now.
"We wanted everything and got nothing. We lost an important player and probably Egypt lost for the World Cup an important player.
"From what I said so far it doesn't look really good."